In recent years, as an electrophotographic photosensitive member used in an electrophotographic apparatus, there has been used an electrophotographic photosensitive member (organic electrophotographic photosensitive member) including an undercoat layer which contains metal oxide particles and an organic compound and a photosensitive layer which is provided on the undercoat layer and which contains a charge generation substance and a charge transport substance.
Potential characteristics (charging property and sensitivity) of the electrophotographic photosensitive member depend on types of materials used for the undercoat layer and the photosensitive layer. In particular, the metal oxide particles and the organic compound used for the undercoat layer are materials which have significant influences on the potential characteristics of the electrophotographic photosensitive member. Accordingly, it has been known that by the structures of the above materials and the combination therebetween, the potential characteristics of the electrophotographic photosensitive member can be improved.
In concomitant with an increase in speed (increase in process speed) of the electrophotographic apparatus, besides improvement in potential characteristics, such as improvement in charging property and improvement in sensitivity, further suppression of the change in potential (change in charging property, and change in sensitivity) during a repetitive use also becomes a subject to be overcome. In particular, the metal oxide particles have a problem in that the change in potential is increased during a repetitive use under a high-temperature and high-humidity environment. The reason for this is believed that the flow of electrical charge is suppressed when the metal oxide particles absorb moisture, and as a result, the potential is changed. Hence, it is necessary to suppress the change in potential by suppression of moisture absorption.
PTL 1 has disclosed that when metal oxide particles and an organic compound having an anthraquinone structure are used for an undercoat layer, the amount of change in residual potential after discharging in a repetitive image formation test under a high-temperature and high-humidity environment can be suppressed.